The present invention relates generally to wireless communication systems and, more particularly, to methods and systems for overlaying narrowband carrier frequencies and wideband carrier frequencies while maintaining system interference at acceptable levels.
The principle of using radio frequencies for wireless communications between two or more communication devices has been known for many years. Over the past several years, many wireless radio communication devices have been created such as pagers, cellular phones, and modems. In the near future, many more devices will be developed and marketed to take advantage of wireless communication. The number of radio carrier frequencies allocated for use is finite and the frequency allocation is controlled by the Federal Communications Commission (xe2x80x9cFCCxe2x80x9d) in the United States. Therefore, the carrier frequencies allocated for radio communication must be optimally arranged to allow many users to simultaneously access a wireless communication system without experiencing interference.
In many systems, each wireless communication device is set up for radio communication by assigning a unique pair of carrier frequencies to the device when it is active. One of the carrier frequencies is used by the communication device to send data to a base station and the other carrier frequency is used by the base station to send data to the communication device. These carriers usually have an assigned bandwidth, which may be something like 30 kHz, for example. Therefore, during operation of the communication device, two different carrier frequencies are being used to send and receive data over the wireless communication network. This scheme is generally known as frequency division multiplexing (FDMA) and is the basis of a majority of wireless communication systems in operation, including analog cellular systems.
As in broadcasting, a carrier frequency is defined by its center frequency and bandwidth. The bandwidth of the carrier frequency represents a continuous range of frequencies or wave lengths that are designated by the lowest and highest frequency. Essentially, bandwidth is a measure of the amount of spectrum space a carrier frequency occupies.
Three multiple access methods are widely used or proposed; they are (1) the previously discussed FDMA system, where each carrier is occupied by a single user; (2) time division multiple access (TDMA), where each carrier is shared by a number of users, and each user exclusively occupies a time slot of the carrier; and (3), code-division multiple access (CDMA), where each carrier is shared by a number of users, and each user exclusively occupies a code, or spreading sequence that defines a carrier frequency. Note that most TDMA and CDMA systems use many carriers, and thus share that feature with pure FDMA systems. An example of a FDMA system can be found in a traditional analog cellular system, while CDMA and TDMA systems are commonly found in digital systems.
The CDMA communication protocol is used for microwave point-to-point communications, satellite communications, and military communications. With CDMA, each user of the wireless communication system is assigned a unique code to differentiate among users of the system. CDMA is based on the principle of direct sequence and is a wideband spread spectrum technology. The CDMA carrier frequency is reused in every cell of the system and each communication device in the cell is assigned a unique code.
TDMA is another example of spread spectrum technology that allows multiple users to occupy the same carrier frequency. The TDMA format used in the United States follows the IS-54 and IS-136 standards and is referred to as the North American digital cellular (xe2x80x9cNADCxe2x80x9d) format. IS-54 and IS-136 use the same carrier frequency bandwidth as analog cellular, namely 30 kHz, for each carrier frequency. As such, TDMA uses a narrowband carrier frequency to conduct radio communication between communication devices. TDMA gives wireless communication systems the ability to operate with three to six users sharing the same carrier frequency at the same time.
Spread spectrum is a term that is used to describe a wide variety of different technology platforms in wireless communication. A spread spectrum system is any communication system that deliberately occupies more bandwidth than the minimum required for data transfer. Spread spectrum systems offer good immunity to noise and interference.
As previously stated, the frequency spectrum allocated for public use in the United States by the FCC is limited to a finite range. Presently, all over the world, there is a substantial increase in the number of wireless communication devices. As such, a need exists for methods and systems that can maximize the number of users that can simultaneously access a wireless communication system without experiencing excessive interference. The solution to this problem must be able to account for, and handle, each of the described basic multiple access technologies used for radio communication. The present invention concerns methods and systems for wireless communications which overlay available narrowband carrier frequencies of TDMA and FDMA systems with the wideband frequencies of CDMA systems to maximize the number of users capable of using the wireless communication systems.
The present invention relates to methods and systems for wireless communication wherein a plurality of narrowband carrier frequencies of TDMA or FDMA systems is overlaid with direct sequence wideband carrier frequencies of a CDMA system. The narrowband carrier frequencies are preferentially selected by frequency hopping to be at the edges of the bandwidth of the wideband carrier frequencies. The frequency hopping is based on the load of the wireless communication network and is implemented by controlling the transmitter to preferentially select the edges of the bandwidth of the wideband carrier frequencies to conduct wireless communication between the devices using the narrowband carrier frequencies. This reduces the interference experienced by the wideband carrier frequencies.
Frequency hopping is a means by which data communication on one carrier frequency is transferred over a period of time to a different predetermined carrier frequency. In the invention, a control system continuously preferentially maximizes radio communication on a narrowband carrier frequency having a center frequency closest to the edge of the bandwidth of the plurality of wideband frequencies.